iommu/mediatek-v1: Allow building as module

This patch only adds support for building the IOMMU-v1 driver as module.
Correspondingly switch the config to tristate and update the iommu_ops's
owner to THIS_MODULE.
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Link: https://lore.kernel.org/r/20210326032337.24578-1-yong.wu@mediatek.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/Kconfig

@@ -364,7 +364,7 @@ config MTK_IOMMU
 	  If unsure, say N here.
 
 config MTK_IOMMU_V1
-	bool "MTK IOMMU Version 1 (M4U gen1) Support"
+	tristate "MediaTek IOMMU Version 1 (M4U gen1) Support"
 	depends on ARM
 	depends on ARCH_MEDIATEK || COMPILE_TEST
 	select ARM_DMA_USE_IOMMU

drivers/iommu/mtk_iommu_v1.c

@@ -20,6 +20,7 @@
 #include <linux/iommu.h>
 #include <linux/iopoll.h>
 #include <linux/list.h>
+#include <linux/module.h>
 #include <linux/of_address.h>
 #include <linux/of_iommu.h>
 #include <linux/of_irq.h>
@@ -529,6 +530,7 @@ static const struct iommu_ops mtk_iommu_ops = {
 	.def_domain_type = mtk_iommu_def_domain_type,
 	.device_group	= generic_device_group,
 	.pgsize_bitmap	= ~0UL << MT2701_IOMMU_PAGE_SHIFT,
+	.owner          = THIS_MODULE,
 };
 
 static const struct of_device_id mtk_iommu_of_ids[] = {
@@ -691,9 +693,7 @@ static struct platform_driver mtk_iommu_driver = {
 		.pm = &mtk_iommu_pm_ops,
 	}
 };
+module_platform_driver(mtk_iommu_driver);
 
-static int __init m4u_init(void)
-{
-	return platform_driver_register(&mtk_iommu_driver);
-}
-subsys_initcall(m4u_init);
+MODULE_DESCRIPTION("IOMMU API for MediaTek M4U v1 implementations");
+MODULE_LICENSE("GPL v2");